Pyroborate-containing jet fuel compositions



United States Patent 3,009,798 PYROBORATE-CONTAINING JET FUEL COMPOSITIONS Glenn E. Irish, Detroit, Mich., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 27, 1956, Ser. No. 580,991 8 Claims. (Cl. 52-.5)

This invention relates to new jet fuel compositions characterized by high thermal stability.

Fuel temperatures in modern jet aircraft power plants are becoming so high that harmful deposits are formed in the pre-combustion phase of the fuel system. Contributing to this has been the use of the fuel as a heat sink to aid in lubricating oil cooling, which has increased fuel temperatures to the point where deposits are so severe that they interfere with normal fuel combustion as well as lubricating oil temperature control. This is so serious a problem that it can eventually lead to engine failure of the turbine section due to uneven temperature patterns. In fact, it is considered the outstanding problem in jet fuels at the present time. Attempts have been made to counteract this by re igning and by the use of shielding materials to minimize heating of the fuel. These methods are uneoonomical and also contribute substantially to the over-all weight of the aircraft.

An object of this invention is to alleviate the thermal stability problems in jet fuels. Another object is to provide new jet fuel compositions which are characterized by a high degree of thermal stability. A further object is to provide processes of inhibiting deterioration of jet fuel normally tending to occur at elevated temperatures below the cracking temperature of the fuel. Other objects will be apparent from the ensuing description.

The above and other objects of this invention are accomplished by providing jet fuel containing from about 0.005 to about percent by weight of a bis-alkylene pyroborate in which each alkylene group contains from 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length. Such compositions, as will be seen below, have a thermal stability of a magnitude which is well beyond that now possessed by any other commercial fuel.

It is known that conventional jet fuel normally tends to deteriorate when subjected to the condition of elevated temperatures below the cracking temperature of the fuel, i.e., temperatures in the range of about 300 to about 500 F. Thus, a part of this invention is the process of inhibiting such deterioration which comprises subjecting a jet fuel containing from about 0.005 to about 5 percent by weight of a bis-alkylene pyroborate as above defined to said condition. Thus, enhanced thermal stability of jet fuel is achieved by blending with a jet fuel from about 0.005 to about 5 percent by weight of a bis-alkylene pyroborate as defined above and subjecting the resulting fuel to the above condition.

The bis-alkylene pyroborate jet fuel additives have the formula:

o 0 wherein R is an alkylene group containing from 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length. In other words, these bis-alkylene pyroborates contain a total of from 4 to 40 carbon atoms and possess two alkylene groups which are 2 to 6 carbon atoms in length. These pyroborates are cyclic esters of pyroboric acid which is sometimes known as mesoboric acid. This acid has the formula:

3,009,798 Patented Nov. 21, 1961 ice Thus, the jet fuel additives of this invention are esters between one equivalent weight of pyroboric acid and two equivalent weights of dihydroxyalkane containing from 2 to 20 carbon atoms, the two hydroxyl groups of which are separated -by from 2 to 6 carbon atoms. Such alkane can also be substituted with other hydrocarbon groups, such as alkyl, cycloalkyl, aralkyl, aryl, and alkaryl. Generally speaking, the nature of such substituents in the alkane is immaterial so long as the total number of carbon atoms in the alkane is no greater than 20. The alkylene groups of the pyroborate esters can also contain one nitrogen atom; iminodiethylene, iminodipropylene, iminodiisopropylene, N-ethyl iminodiethylene, etc., serving as examples. These particular pyroborates are thus formed from two equivalent weights of a diol, such as diethanol amine, dipropanol amine, diisopropanol amine, N-ethyl diethanol amine, etc., per equivalent weight of pyroboric acid.

Preferred jet fuel additives of this invention are hisalkylene pyroborates containing a total of from 6 to 16 carbon atoms wherein each alkylene group is from 2 to 3 carbon atoms in length and is substituted with from 1 to 4 alkyl groups containing from 1 to 2 carbon atoms. These preferred pyroborates are thus bis-alkylene pyroborates having two 5- or 6-membered rings composed of two or three carbon atoms, two oxygen atoms and one boron atom. These pyroborates are preferred because they are miscible in all proportions with most jet fuels. Moreover, the 5- or 6-membered rings in these preferred pyroborates impart a high degree of stability to the additives.

Particularly preferred as a jet fuel additive is bis- (l-methylethylene) pyroborate. This compound not only possesses the excellent attributes of the preferred class of additives of this invention, but is easily made from propylene glycol (1,2-dihydroxypropane) which is inexpensive and readily available. Thus, this most particularly preferred additive of this invention is very stable, very highly-soluble in jet fuels, easily made, and cheap. Furthermore, it contains a high proportion of boron in the molecule.

The additives of this invention are more resistant to hydrolysis than most esters of boron acids known heretofore. This enhances the utility of the present pyroborate esters as additives to jet fuels because these esters, when dissolved in jet fuel, are not rapidly decomposed on contact with moisture which is normally present in most commercial jet fuels. The hydrolysis resistance of the present additives is attributable, at least in part, to the presence therein of the alkylene bridges. This, in itself, is surprising because these alkylene bridges are insutiicient to sterically hinder the entire molecule.

Another outstanding feature of the additives. of this invention is the fact that even when, under drastic conditions, they are hydrolyzed the hydrolysis products thereof are themselves extremely resistant to hydrolysis and very soluble in the jet fuel. Consequently, even though a jet fuel composition of this invention is agitated with large quantities of water, the boron dissolved in this fuel remains in solution in a suitable chemical form and continues to exert its beneficial functions. Furthermore, such drastic hydrolysis conditions do not result in the formation of insoluble sludges or other residues which would normally occur when using prior boron additives in jet fuels.

Still another feature of this invention is the fact that the present additives are easily made and inexpensive. Thus, this invention enables substantial improvements in the performance characteristics of the jet fuels at low cost.

The jet fuels, the thermal stability of which are greatly improved pursuant to this invention, are principally bydrocarbon fuels which are heavier than gasoline, i.e., distilled liquid hydrocarbons fuels having a higher endpoint 11 gasoline. In general, the jet fuels can be comsed of distillate fuels and naphthas and blends of the we, including blends with lighter hydrocarbon fracas, so long as the endpoint of the final jet fuel is at st 435 F. and preferably greater than 480 F. It will understood, however, that the jet fuels which are emyed according to this invention can contain certain ier ingredients, such as alcohols or the like, provided resulting fuel blend meets the specifications imposed on jet fuels. However, the jet fuels of this invention free of organometallic additives because such additives erfere with the ability of the pyroborates to improve the :rmal stability properties of the fuels. Thus, an organotallic additive, if present in the jet fuel, would counterthe effectiveness of the pyroborate additive and render jet fuel at least as thermally unstable as it would in the absence of any additive. This counteraction of ectiveness is attributable, at least in part, to the thermal gradation of the organometallic additive itself and the nsequent insoluble degradation products which form.

Typical jet fuels improved according to this invention :lude JP-3, a mixture of about 70 percent gasoline and percent light distillate having a 90 percent evaporated int of 470 F.; JP-4, a mixture of about 75 percent soline and 35 percent light distillate, a fuel especially signed for high altitude performance; JP-S, an espetlly fractionated kerosene; low freezing point kerosene,

The following are specifications of typical liquid hydrorbon jet fuels of this invention:

Fuel E Fuel F Fuel). Fuel B Fuel 0 FuelD (JP-4 (kero- (J P-3) (J P-) (J P-5) (JP-4) refsene) ereelr 7 evaporated, F. 160 220 395 221 380 ievaporated, F. 470 470 480 379 460 480 idpolnt F 600 550 550 480 516 avlty, API.. 50 as 41.3 48. 5 4a :lstent gum, mg. .00 ml., max 7 7 7 1.0 1.4 1.7 0 tentlnl gum, ng.l100 mL, max 14 14 14 1. 0 B. 6 aid vapor presllll'fl, p.s.L 7.0 3.0 omat-lcs, vol. Jereent 25.0 25. 0 25. 0 12. 5 14. 6 14.3 eflns, vol per The following examples illustrates various specific em- )diments of this invention.

Example I To 100,000 parts of Fuel A is added with stirring five ms (0.005 percent) of bis-ethylene pyroborate dissolved l parts of toluene. The resulting fuel is found to assess improved thermal stability characteristics.

Example II Example IV To 100,000 parts of Fuel D is added 500 parts (0.5 perent) of bis-(1,2-dimethylethylene) pyroborate. The reulting fuel blend is found to possess superior thermal tability characteristics.

Example V To 100,000 parts of Fuel E is added 40 parts (0.04

600 parts of benzene. The resulting fuel blend possesses enhanced thermal stability properties.

Example VI To 100,000 parts of Fuel F is added 200 parts (0.2 percent) of bis-hexamethylene pyroborate dissolved in 5000 parts of toluene. After mixing, the resulting fuel blend is found to possess enhanced thermal stability properties.

. Example VII Fuel C is blended with a lighter hydrocarbon fraction to give a final jet fuel having an endpoint of 435 F. 100,000 parts of this fuel is treated with 20 parts (0.02 percent) of bis-(l,4-dirnethyltetramethylene) pyroborate. The resulting clear fuel possesses outstanding thermal stability characteristics.

Example VIII To 100,000 parts of a liquid hydrocarbon jet fuel having an endpoint of 550 F. is added 100 parts (0.1 percent) of bis-(2,3-dimethyltetramethylene) pyroborate. The resulting clear jet fuel containing this pyroborate possesses eminently superior thermal stability properties.

Example IX To 100,000 parts of Fuel A is added 15 parts (0.015 percent) of bis-(l,1,3-trimethyltrimetl1ylene) pyroborate. This fuel, after mixing, possesses outstanding thermal stability characteristics.

Example X Example XII To 100,000 parts of Fuel B is added with stirring 10 parts (0.01 percent) of bis-(l-methyl-2-cyclohexyl-4-nbutyltrimethylene) pyroborate. The resulting jet fuel is found to possess outstanding thermal stability characteristics.

Example XIII To 100,000 parts of Fuel D is added 100 parts (0.1 percent) of bis-(2-benzyltrimethylene) pyroborate. After stirring, the resulting clear fuel possesses enhanced thermal stability characteristics.

Example XIV To 100,000 parts of Fuel F is added 600 parts (0.6 percent) of bis-(1,4-(m-tolyl)tetramethylene) pyroborate. After stirring, the resulting fuel blend is found to possess outstanding thermal stability properties.

Example XV To 100,000 parts of Fuel A is added 100 parts (0.1 percent) of bis-(l-methyl-Z-ethylethylene) pyroborate. The resulting fuel possesses improved thermal stability characteristics.

Example XVI To 100,000 parts of Fuel 0 is added 500 parts (0.5 percent) of bis-(l,1,3,3-tetramethyltrimethylene) pyroborate. The resulting fuel blend possesses outstanding thermal stability characteristics.

Example XVII To 100,000 parts of Fuel C is added 200 parts (0.2

percent) of bis-( l-methyltrimethylene) pyroborate. The resulting fuel possesses outstanding thermal stability proplercent) of bis-tetramethylene pyroborate dissolved in erties.

Examples IV, IX, XV, XVI and XVII illustrate preferred jet fuel compositions of this invention containing preferred bis-alkylene pyroborates. A particularly preferred jet fuel of this invention is illustrated by Example II, since the fuel in this example contains bis-(l-methylethy1ene)-"'pyroborate.

The substantial improvements which result from addition of bis-alkylene pyroborates, as described above, to jet fuel is illustrated by tests in an apparatus known as the Erdco Fuel Coker. See Petroleum Processing, December 1955, pages 1909-1911. The apparatus consists of a heated, sintered steel filter through which a preheated fuel is passed at a regulated rate. The time which it takes for the pressure drop across the filter to reach 25 inches of mercury is taken as a measurement of the coking tendencies of the fuel and, therefore, as a measurement of the thermal stability characteristics of the fuel. A fuel that runs through the apparatus for a full 300 minutes without causing any pressure drop is considered completely, thermally stable. The ideal fuel would pass through the filter indefinitely without causing any pressure drop.

To demonstrate the substantial improvements in high temperature stability exhibited in jet fuels of this invention, recourse is had to the above Erdco Coking test. Samples of jet fuels of this invention, such as those appearing in the above examples, are subjected to the Erdco Coking test. The conditions used in this test are as follows: Unit operated at 150 p.s.i. with the preheater temperature at 325 F., the filter temperature at 500 F., and a residence time of 30 seconds. For comparative purposes, the corresponding pyroborate-free base fuels are likewise subjected to this test. It is found that in all instances the presence in the fuels of the pyroborate causes a substantial increase in the time required for a pressure drop of 25 inches of mercury across the filter to occur. Furthermore, the majority of the fuels of this invention formulated from base fuels requiring at least 150 minutes for this pressure drop to occur do not reach this pressure drop even in the full 300 minutes. In some cases, the pressure drop achieved with these last-named jet fuels of this invention is less than 10 inches of mercury after 300 minutes.

As an example of the outstanding potency of bis-alkylene pyroborates in improving the high temperature stability characteristics of jet fuels, comparative Erdco Coking tests were conducted under the conditions specified above. The base fuel used was a JP-4 referee fuel having the following inspection data:

When this additive-free base fuel was tested for its thermal stability in a pair of tests, it was found that a pressure drop of 25 inches of mercury occurred after 27 and 32 minutes. Two individual portions of this same base fuel, each containing 0.17 percent by weight of bis-(l-methylethylene) pyroborate, were then subjected to the same coking test. It was found that a pressure drop of 25 inches of mercury did not occur until after 89 and 8 minutes. Thus, this typical fuel of this invention poi sessed a thermal stability almost 300 percent as great a the corresponding pyroborate-free base fuel. The magn: tude of this improvement is particularly outstanding'i view of the very poor thermal stability of the base fue Similar results are obtained with other jet fuel C011. positions of this invention, i.e, hydrocarbon jet fuels cor taining from about 0.005 to about 5 percent by weight (1 10 any pyroborate described by the general formula a;

pean'ng above.

The jet fuel compositions of this invention possess out standing high temperature stability characteristics by th presence therein of such additives as bis-tetramethylene pyroborate,

and the like. Preferred additives of this invention includ bis- 1-ethylethylene)pyroborate, bis 1,1,2,2-tetramethylethylene)pyroborate,

bis-( 1,2rdimethyl-2-ethylethylene) pyroborate,

bis-(1-methyl-3-ethyltrimethylene) pyroborate,

and the like. Bis-(l-methylethylene) pyroborate is pa ticularly preferred. The additives of this invention are prepared by heatir boric oxide (B 0 with an appropriate acyclic diol mee ing the requisites set forth above, in the presence of z azeotroping solvent to remove the water formed durir the reaction. One molecular equivalent of boric oxide 40 reacted with each two molecular equivalents of the di present and in the process two molecular equivalents 1 water are removed as an azeotrope with the solvent. Sui able azeotroping solvents include benzene, toluene, xylen natural hydrocarbon fractions boiling in the range 1 about 75 to 150" C., or the like. This mixture of bor oxide, diol and azeotroping solvent is thus heated to tl reflux temperature75 to 150 C. On completion the reaction, as evidenced by cessation of water evol tion, the resulting product comprises the pyroborate est dissolved in the azetroping solvent. If desired, the pyr borate ester can then be recovered from the solutit by distilling off the solvent. The pyroborate ester 1 maining in the distillation vessel can then be purified l vacuum distillation if desired. 0n the other hand, t solution of the pyroborate in the azeotroping solvent which it was formed is a very useful formulation for u in subsequent blending operations with jet fuels. A f1 ther advantage of using this solution is that it enhanc the stability of the pyroborate ester. Thus, by using su solutions, the presence of the desired quantity of t 6 pyroborate ester in the resulting jet fuel blend is assurt none of the pyroborate ester has been decomposed ev when this solution has been stored for long periods time.

The amount of bis-alkylene pyroborate used in the fuels of this invention can range from about 0.005 p cent to about 5 percent by weight. Ordinarily, amou' of 0.01 to 0.2 percent are found to be quite effecti Variations from these concentration ranges are perrr sible. For example, in jet fuels initially possessing a i degree of thermal stability, very small amounts of above pyroborates are suflicient to greatly improve thermal stability characteristics of such fuels. On other hand, where the jet fuel initially has a very p4 thermal stability, larger amounts (about 4 to 5 perc by weight or more) can be effectively used.

I claim: I

1. Jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., containing from about 0.005 to about 5 percent by weight of a bis-alkylene pyroborate in which each alkylene group contains from 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length.

2. Jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., containing from about 0.005 to about 5 percent by weight of bis-alkylene pyroborate containing a total of from 6 to 16 carbon atoms wherein each alkylene group is from 2 to 3 carbon atoms in length and is substituted with from 1 to 4 alkyl groups containing from 1 to 2 carbon atoms.

3. Jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., containing from about 0.005 to about 5 percent by weight of bis-(l-methylethylene) pyroborate.

4. The composition of claim 1 in which the pyroborate is bis-(trimethylene)pyroborate;

is bis-(l,l,3-trimethyltrimethylene)pyroborate.

7. The composition of claim 1 in which the pyroborate is bis-(1,1,3,3-tetramethy-ltrimethylene)pyrcborate.

8. A process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer with said lubricating oil a thermally stabilized jet fuel consisting essentially of distilled liquid hydrocarbon fuel having an end point of at least 480 F., said end point being higher than that of gasoline, said fuel containing from about 0.005 to about 5 percent by weight of a his alkylene pyroborate in which each alkylene group contains from 2-20 carbon atoms and is from 2-6 carbon atoms in length.

References Cited in the file of this patent UNITED STATES PATENTS 2,710,252 Darling June 7, 1955 2,741,548 Darling et al. Apr. 10, 1956 2,767,069 Fay et a1. Oct. 16, 1956 

1. JET FUEL CONSISTING ESSENTIALLY OF DISTILLED LIQUID HYDROCARBON FUEL HAVING A HIGHER END POINT THAN GASOLINE, SAID END POINT BEING AT LEAST 480*F., CONTAINING FROM ABOUT 0.005 TO ABOUT 5 PERCENT BY WEIGHT OF A BIS-ALKYLENE PYROBORATE IN WHICH EACH ALKYLENE GROUP CONTAINS FROM 2 TO 20 CARBON ATOMS AND IS FROM 2 TO 6 CARBON ATOMS IN LENGTH. 